Wheeled platforms

ABSTRACT

A wheeled platform ( 100 ) is disclosed, which is characterized by high mobility and reliability, and which can be used in a wide range of applications including transport and robotic devices. The platform has fore and aft body portions ( 130, 132 ), each body portion with first and second side portions ( 103, 104 ). Overlapping wheels ( 112, 114, 116, 118 ) are rotatably attached to the port-side portion ( 106 ) and overlapping wheels ( 120, 122, 124, 126 ) are rotatably attached to the starboard-side portions. The fore body portion ( 130 ) can be connected to the aft body portion ( 132 ) via an articulation element ( 133 ).

CITATION OF PROVISIONAL APPLICATION

[0001] This application for patent is a non-provisional applicationclaiming the priority of U.S. provisional application for patent SerialNo. 60/194,922 filed Apr. 4, 2000.

FIELD OF THE INVENTION

[0002] The present invention relates to wheeled platforms and wheeledvehicles in general, and in particular, relates to apparatus,configurations and methods for providing highly mobile wheeled platformssuitable for a variety of uses, including, but not limited to, roboticdevices.

BACKGROUND OF THE INVENTION

[0003] The application of robotic devices and general-purpose transportplatforms has enjoyed enormous growth in recent years, across allsectors of industrial, military and consumer/household operations, for arange of tasks limited only by the imagination of those employing suchdevices. These have included such disparate applications assurveillance, bomb disposal, industrial maintenance and householdchores. In response to these demands, a number of configurations havebeen developed to provide enhanced mobility vehicle structures that canbe used in transport and robotic device applications over rough surfacesor terrain. Representative examples of such configurations are disclosedin the following U.S. Pat. Nos.:

[0004] 6,144,180

[0005] 5,833,248

[0006] 5,742,975

[0007] 5,579,857

[0008] 5,515,934

[0009] 5,507,358

[0010] 5,323,867

[0011] 4,993,912

[0012] 4,932,491

[0013] By way of example, U.S. Pat. No. 6,144,180 discloses a robothaving a body, a pair of lift arms mounted pivotally on the body, a pairof leg support arms mounted pivotally on the lift arms, and a pair ofwheeled leg assemblies mounted pivotally on each of the leg supportarms. Each of the leg support arms is rotatable to turn one of thewheeled leg assemblies, which rests on the ground at the back of theother one of the wheeled leg assemblies, to a position in front of theother one of the wheeled leg assemblies, thereby moving forward therobot body. The lift arms can be rotated upward or downward relative tothe leg support arms to lift or lower the robot body.

[0014] U.S. Pat. No. 5,833,248 purports to show a stairwayascending/descending vehicle that can ascend or descend stair-stepshaving a height greater than the diameter of the vehicle's wheels. Thevehicle has mainshafts rotatably supported on a front portion and a rearportion of a vehicle body, respectively. Front arm members are mountedto the front mainshafts; rear arm members are mounted to the rearmainshaft; and the front and rear arm members are configured to rotatewith respect to the mainshafts.

[0015] U.S. Pat. No. 5,742,975 discloses an articulated vehicle forscrubbing floor surfaces defined by intersecting aisles of relativelynarrow width. The vehicle has articulated portions that facilitate turnsin narrow aisles.

[0016] U.S. Pat. Nos. 5,579,857 and 5,507,358 disclose stair-climbingvehicles having a body, front and rear wheels provided at the front andrear of the vehicle body, respectively, front and rear auxiliary wheelsfor lifting the front and rear wheels, respectively, by one stair-step,a driving unit for driving each wheel, a pivoting unit for pivoting thefront and rear auxiliary wheels, sensors for detecting a riser portionof stairs, and a control unit for controlling the driving unit and therotating unit in accordance with outputs of the sensors. It is claimedthat since the vehicle ascends/descends stairs by rotation of theauxiliary wheels, a comer portion of the step of stairs is not damagedwhile the vehicle goes up and down stairs.

[0017] U.S. Pat. No. 5,515,934 discloses a modular robot body assemblysegmented into five modules, symmetrically located around a horizontalcenter shaft system, enabling the robot body, front legs, and back legsto rotate about a horizontal center axis with respect to one another.

[0018] U.S. Pat. No. 5,323,867 discloses a robot transport platformadapted for locomotion, having a base with three wheels on each side.The wheels near the fore and aft ends are omnidirectional in design,while the intermediate wheel (between the omnidirectional wheels) is aconventional wheel. The omnidirectional wheels have staggered rows ofspherical rollers rotatably mounted to the circumference of the wheel'shub. Torque is provided by two electric motors independently operatingthe wheels on each side, and is transferred to the wheels via a gearbox, a chain, and cogged drive belts.

[0019] U.S. Pat. No. 4,993,912 discloses a stair climbing robot having achassis with powered, opposed front wheels and two pairs of rear wheels,each pair being rotatably mounted on a beam at opposite ends thereof,and each beam being rotatably mounted on the chassis. A drive motor isprovided for driving each pair of wheels in the same direction at apredetermined rotational velocity; and a drive means is provided forsimultaneously rotating the beams at a predetermined rotational velocityand in a predetermined direction. In operation, the beams rotate forwardwhile each pair of rear wheels rotates in an opposite direction at thesame rotational velocity. Forward movement is thus powered by the frontwheels and rotating beams, while the rotational velocity of the rearwheels relative to the terrain is zero.

[0020] U.S. Pat. No. 4,932,491 describes a vehicle having auxiliarywheels that can be deployed to avoid overturning the vehicle whenturning, traversing a slope, climbing an embankment or the like, and toright the vehicle when it is overturned.

[0021] Although the above-described devices represent advances overprevious designs, wheeled platforms and devices such as those disclosedin the above-listed U.S. patents have notable limitations. They aretypically inefficient, complex, cumbersome, heavy, and poorly suited tohigh-mobility operations on rough terrain or surfaces, such astraversing steep slopes, maneuvering around obstacles, and ascending ordescending ramps or stairs.

[0022] Accordingly, there exists a need for wheeled platforms bettersuited to high-mobility, high-agility applications on rugged terrain andsteep pitches. Ideally, such structures would be relatively robust,reliable, and conservative of battery or other energy sources, whileproviding enhanced abilities to traverse challenging terrain, and insome instances, to ascend or descend stairs and other obstacles. It isalso desirable that such platforms be relatively compact, but scalableby selection of components and overall dimensions to adapt to variousexpected (and unexpected) terrain requirements.

SUMMARY OF THE INVENTION

[0023] The present invention provides wheeled platforms characterized byhigh mobility and reliability, which are readily used in a wide range ofapplications including transport and robotic devices. The wheeledplatforms described herein can be operated on rough or steep terrain orsurfaces; can ascend and descend conventional (and non-standard) stairs,whether indoors or outdoors; and can climb steep pitches smoothly. Onstairs, the disclosed platforms can climb and descend with a minimum ofstep-induced dynamics, such as heave, pitch, and roll.

[0024] In addition, the disclosed platforms can turn-in-place (with aturning circle coextensive with the platform), are efficient,conservative of energy usage, and relatively simple in construction, andthus relatively inexpensive and lightweight.

[0025] The wheeled platforms described herein can be scaled (bycomponent selection and overall dimension) so as to pass throughstandard doorways, crawl under standard furniture, and ensure low powerconsumption. In such embodiments, the wheeled platforms can includemotive elements (whether electric, internal combustion or other) so thatthe platforms can propel themselves on level, uneven, or hilly ground,or over thresholds; and can maneuver on level terrain or on stairs,turning or changing direction as needed or directed.

[0026] A feature of the disclosed platforms is their ability to climbstairs with a rise per step on the same order of dimension as thediameter of a wheel element.

[0027] A number of overall configurations of wheeled platforms aredisclosed herein. In a first configuration, a plurality of wheels arearrayed on either side of a body or base element, with wheel diameterand wheel spacing (or axle spacing) selected to enable the platform totraverse terrain elements, including stairs.

[0028] In another configuration, the wheeled platform is equipped withan articulated tail element that can be controlled to make selectivecontact with terrain.

[0029] In yet another configuration, the platform is articulated forrelative movement of a first, forward body portion (referred to as a“flipper”) and second, rearward body portion (referred to as a “base”)about a substantially horizontal axis of rotation. The flipper can becontrolled to make selective contact with terrain.

[0030] In each of these configurations, wheel spacing can be selected toprovide fore/aft overlap of the wheel elements; selective rocker of thewheels can be provided to facilitate turn-in-place and efficientmovement over level terrain; independent port and starboard drives canbe provided to enable maneuvers, turns, or turns-in-place; andintermediate wheel elements (in plan view) can be mounted outwardmost,to enable turning-in-place in limited spaces. In addition, deeplystudded or scalloped wheel elements can be employed at selected wheellocations, to facilitate gripping of stair-steps.

[0031] Thus, in one aspect, the invention can be embodied in a wheeledstructure in which first and second sets of wheel elements are rotatablyattached, respectively, to first and second portions of a platform orbody, wherein a portion of at least one wheel element overlaps a portionof at least one other wheel element in the same set of wheel elements.This overlap (which in one embodiment can be termed “fore/aft overlap”)can be further defined in that each wheel element has a defined radius(which need not be equal for all wheel elements), and a portion of atleast one wheel element in a set of wheel elements overlaps anotherwheel element by a predetermined fraction of the radius of the otherwheel element. In other words, the spacing between at least two wheelelement axes will be less than the sum of the respective radii of thewheel elements. In an embodiment having equal-sized overlapping wheelelements (a constraint that is not required to practice the invention)the distance between the axes of one wheel element and another wheelelement on the same side of the platform will be less than the diameterof the wheel elements. The wheeled structure thus defined can have 2, 3,4, 5 or more axles, with 4, 6, 8 or more wheel elements (or even, insome embodiments, an odd number of wheel elements).

[0032] In another aspect of the invention, at least one of theintermediate wheel elements on each side of the wheeled structure(whether there are one or more intermediate wheels per side) aredisplaced outwardly from a longitudinal centerline of the body by anamount greater than that of any end wheel element. In other words, inplan view, the centermost wheel or wheels elements have a wider “track”than the end wheel elements—i.e., the port-side and starboard-sidecenter wheels, in plan view, are displaced outwardly from the body,relative to other wheels in the respective first and second sets ofwheel elements. This increases the stability of the wheeled platform,while enabling the platform to turn-in-place within a circle defined bythe radii of the outer corners of the platform.

[0033] It will be noted that in the following detailed description andin the claims, the term “at least one intermediate wheel element” isused to denote one, two, three or more wheels per side (port andstarboard or left and right) that are longitudinally between “outer” or“corner” wheel elements. Similarly, the outboard or corner wheelelements can number four or more. In an embodiment having four wheels,selected wheel elements can be arbitrarily designated as intermediatewheel elements. As the wheeled platform of the instant invention has nosingle direction of travel, the designations of left and right (in theviewer perspective) or port and starboard (in the coordinate system ofthe predominate direction of travel) are arbitrary and merely denoteopposite sides of the body.

[0034] In one aspect of the invention, a selected degree of rocker isprovided, such that the point of contact of the centermost wheel elementon each side of the body can be lower than the respective point ofcontact of the end wheel elements. This facilitates the wheeled platformspinning or turning-in-place, thereby increasing agility. It will beunderstood by one of skill in the art that while in one embodiment,rocker of the wheel arrangement permits only one or two wheel-elementpairs to contact a ground plane, in an alternate embodiment, the pointof contact can be coplanar for all the wheels, depending on theweighting of the platform.

[0035] In another aspect of the invention, the body of the wheeledplatform includes first and second body portions (which in oneembodiment are fore and aft body portions), wherein the first bodyportion is connected to the second body portion via an articulationjoint. The joint can be a hinge, pivot, or flexible body portion. Theaxis of articulation of the element can be substantially horizontal. Thearticulation element enables one of the body portions to act as aflipper having selective (and controllable) contact with the terrain, soas to increase the stability of the vehicle when traversing ruggedterrain or climbing or descending stairs. In one embodiment, wheels arerotatably coupled to the flipper, and the flipper can provide support tothe body (or other portion of the body) when traversing difficult orsteep terrain or stairs. Angle control or motion control elements can beprovided to control the angle of the flipper portion relative to thebody (or other portion of the body).

[0036] In a further aspect of the invention, drive elements are providedto drive the wheel elements. In one embodiment, an independent driveelement is arranged to drive at least one respective wheel element, andcontrol elements are provided for controlling rotation of the respectivewheel elements, to enable forward or reverse platform movement, turns orturns-in-place. In one embodiment, a first set of wheel elements iscoupled to a port side of the body, a second set of wheel elements iscoupled to a starboard side of the body, and independent port-side andstarboard-side drive elements are provided to enable forward andrearward movement, turns or turns-in-place. In another aspect of theinvention, the wheel elements in selected sets (or subsets) of wheelelements (e.g., left or right, port or starboard) can be geared orotherwise mechanically coupled so that the wheels in a wheel set turn inunison.

[0037] The wheel elements utilized in connection with the invention caninclude a tread portion; and in turn, the tread portion can be eithersmooth or patterned (e.g., with a studded or scalloped pattern). Inother embodiments, wheel elements can be smooth or patterned withstudded or scalloped patterns (without a distinct or separable treadportion). One such pattern thus consists of raised, spaced apart blocks.Another practice of the invention utilizes scalloped wheel elements atthe corners of the platform (assuming more than 4 wheels) and smoothwheel elements for at least one of centermost wheel elements on eachside. This facilitates turn-in-place, while maintaining theterrain-handling advantages (e.g., stair-climbing) afforded by scallopedwheel elements.

[0038] Finally, in the case of platforms useful in stair-climbing anddescending, it has been found that the selection of wheel elementdiameter, axle count and axle spacing can and should be made inaccordance with particular mathematical functions set forth hereinafter.

[0039] In alternative embodiments of the invention, fore/aft wheelelement overlap is not utilized, but instead, wheel element diameter,wheel spacing, platform-to-wheel spatial displacement, and in oneembodiment, flipper dimensions, are selected such that the platform issufficiently high to avoid contact with obstacles or terrain elements,such as stairs. In particular, the wheels in this embodiment aredisposed sufficiently close together (but without overlap) such that thevehicle can transverse stairs, rocks, thresholds or other obstacles (insome instances, by employing a flipper element), while maintaining theplatform at a sufficient ground clearance to avoid ground/obstaclecontact.

[0040] Additional features of the invention, its nature and variousadvantages are shown and described in the accompanying drawings andwritten description. The written description and attached drawingfigures present the invention at various levels of enabling detail, fromconceptual to specific examples of implementation. It will beappreciated by those skilled in the art that the present invention maybe practiced in connection with details that differ from the specificexamples of implementation set forth herein. By way of example, thoseskilled in the art will appreciate that the methods, systems and devicesdescribed herein can be implemented in devices, systems and methodsdiffering from those depicted or described herein, and that the examplesset forth herein are provided by way of illustration rather thanlimitation. In other instances, conventional or otherwise well-knownstructures and devices are described by way of reference to known orconventional engineering terminology.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Various aspects and embodiments of the present invention are setforth in the attached drawing figures, in which:

[0042]FIG. 1A is a plan view of one configuration of wheeled platform inaccordance with the invention.

[0043]FIG. 1B is a side view of the wheeled platform of FIG. 1A, showinga first, “flipper” portion of the platform elevated off the groundplane.

[0044]FIG. 1C is another side view of the wheeled platform of FIG. 1A,in which the flipper portion has been lowered to make contact with theground plane.

[0045]FIG. 2 is a front three-quarter view of a robotic device employinga wheeled platform constructed in accordance with the invention.

[0046]FIG. 3 is a three-quarter view of the robotic device of FIG. 2,showing further detail of the wheeled platform constructed in accordancewith the invention.

[0047]FIG. 4 is a side view of the robotic device of FIG. 2.

[0048]FIG. 5 is an isometric view of the wheeled platform utilized inthe robotic device of FIG.2.

[0049]FIG. 6 is a side view of the wheeled platform utilized in therobotic device of FIG. 2.

[0050]FIG. 7 is a plan view of the wheeled platform utilized in therobotic device of FIG. 2.

[0051]FIG. 8 is a perspective view of another embodiment of a wheeledplatform according to the invention, with a “tail” element in aretracted position. FIG. 9 is a perspective view of the wheeled platformof FIG. 8, with the tail element in an extended position. FIG. 10A is abottom view of the wheeled platform of FIG. 8. FIG. 10B is a side viewof the wheeled platform of FIG. 8, showing detail of the drive elements.

[0052]FIG. 11A is a top view of the wheeled platform of FIG. 8, showingthe tail element in a retracted position.

[0053]FIG. 11B is another side view of the wheeled platform of FIG. 8.

[0054]FIG. 11C is a rear view of the wheeled platform of FIG. 8.

[0055]FIG. 12A is a side view of another embodiment of a wheeledplatform in accordance with the invention.

[0056]FIG. 12B is a side view of the wheeled platform of FIG. 12Aascending or descending stairs.

[0057]FIGS. 13A, B, C, D and E are outside, edge-on and perspectiveviews, respectively, of one embodiment of a wheel element suitable foruse in wheeled platforms according to the invention.

[0058]FIG. 14 is a schematic diagram of one embodiment of a wheeledplatform in accordance with the invention ascending or descendingstairs.

[0059]FIGS. 15A, 15B and 15C are further schematic diagrams of oneembodiment of a wheeled platform in accordance with the inventionascending or descending stairs.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS Overview

[0060] The present invention, various embodiments of which are depictedin the attached drawing figures, provides highly agile wheeled platformsthat can be used in various transport and robotic applications andoperated on rough or steep terrain or surfaces. The disclosed platformscan be scaled, by component selection and overall dimension, so as topass through standard doorways, crawl under standard furniture, andensure low power consumption. The platforms can include motive elements(whether electric, internal combustion or other) so that the platformscan propel themselves on level, uneven, or hilly ground, or overthresholds; maneuver on level terrain or on stairs, turning or changingdirection as needed or directed; and spin or turn-in-place, with aturning circle substantially coextensive with the radius of theplatform.

[0061] A number of overall configurations of wheeled platforms aredisclosed herein. In a first configuration, referred to as the “flipper”embodiments, a plurality of wheels are arrayed on either side (e.g.,left/right, port/starboard) of a body or chassis element, and the bodyor chassis is articulated to permit controlled, relative movement of afirst body portion relative to a second body portion about a first axisof rotation. In one embodiment, the first body portion is referred to asa flipper and the second body portion referred to as a “base”; and thefirst axis of rotation is substantially perpendicular to a longitudinal(or fore/aft) axis of the platform. This substantially perpendicularaxis of rotation may be substantially horizontal, and the rotation orvertical movement of the flipper about that axis can be controlled by amotor or the like, so that the flipper can make selective contact withterrain and/or to control pitch, heave and other motions of the baseportion.

[0062] In another configuration, referred to herein as the “tail”embodiments, the wheeled platform is equipped with an articulated tailelement that can be controlled to make selective contact with terrain.In the flipper and tail configurations, the wheel elements can bedisposed about the platform such with selected fore-aft overlap betweenadjacent wheel elements, and such that intermediate wheel elements oneach side are displaced outward from a fore/aft axis of the platform, soas to present a wider track at the fore/aft centerline, thus increasingstability while maintaining the ability of the platform to turn-in-placewithin a small circle. In each of these configurations, wheel diameter,wheel (or axle) spacing and other parameters can be selected to provide,where desirable, fore/aft overlap of the wheel elements. In addition,selective rocker of the wheels can be provided to facilitateturn-in-place and efficient movement over level terrain; independentport and starboard drives can be provided to enable maneuvers, turns, orturns-in-place; and intermediate wheel elements (in plan view) can bemounted outwardmost, to enable turning-in-place in limited spaces. Inaddition, deeply studded or scalloped wheel elements can be employed atselected wheel locations, to facilitate gripping of stair-steps.

[0063] In yet another embodiment, the wheels elements are notoverlapping, but wheel diameter and wheel spacing (or axle spacing) areselected to enable the platform to traverse terrain elements, such asstairs and the like, with or without the use of a flipper portion.

[0064] Finally, discussion will be provided of selection criteria andstair climbing/descending.

Flipper Embodiment

[0065] As depicted in FIGS. 1A, 1B, and 1C, one embodiment of theinvention is a wheeled platform 100 in which first and second sets (102,104) of wheel elements are rotatably attached, respectively, to firstand second portions (in this case, left and right, or port and starboardsides 106, 108) of a body or chassis 110, wherein a portion of at leastone wheel element 112 overlaps a portion of at least one other wheelelement 114 in the same set of wheel elements.

[0066] Thus, for example, in the first, port set (102) of wheel elements1 12, 114, 116, and 118, wheel element 114 overlaps wheel element 112;wheel element 116 overlaps wheel element 114; and wheel element 118overlaps wheel element 116. Similarly, in the second, starboard set(104) of wheel elements 120, 122, 124 and 126, wheel element 122overlaps wheel element 120; wheel element 124 overlaps wheel element122; and wheel element 126 overlaps wheel element 124.

[0067] The platform 100 depicted in FIGS. 1A, 1B, and 1C isadvantageously employed in the iRobot commercially available from iRobotCorporation of Somerville, Mass., various aspects of which, includingfirst and second sets of wheel elements 102,104, and wheel elements112,114, 116, 118,120, 122,124, and 126, are depicted in FIGS. 2-7.However, it will be understood that the structures described herein canbe employed in a wide range of other transport and robotic applications.

[0068] Referring now to FIGS. 1-7, the overlap between adjacent wheels(which in one embodiment can be termed “fore/aft overlap”) can befurther defined in that each wheel element has a defined radius (whichneed not be equal for all wheel elements), and a portion of at least onewheel element in a set of wheel elements overlaps another wheel elementby a predetermined fraction of the radius of the other wheel element. Inother words, the spacing between at least two wheel element axes will beless than the sum of the respective radii of the wheel elements. In anembodiment having equal-sized wheel elements (a constraint that is notrequired to practice the invention) the distance between the axes of onewheel element and another wheel element on the same side of the platformwill be less than the diameter of the wheel elements.

[0069] It will be understood that the elements used to rotatably attachthe wheel elements to the body portions, which may include axles, pins,bearings, hubs and the like, may be conventional in nature, and theindividual selection of particular coupling elements is within theability of those skilled in the art.

[0070] The wheeled platform 100 thus defined can have 2, 3, 4, 5 or more“axles”, with 4, 6, 8 or more wheel elements (or even, in someembodiments, an odd number of wheel elements). The term “axle”, as usedherein, is not limited to a physical axle passing through opposite rightand left wheels, but in preferred embodiments can include an axis ofrotation of individual wheel elements, which, in some embodiments havingport/starboard symmetry, will be common to opposite left and rightwheels. It will be understood, however, that the invention can beembodied in nonsymmetrical forms, in which there will not be a common“axle” passing through both left and right wheels.

[0071] Referring again to FIGS. 1-7, it will be seen that the body 110of the wheeled platform 100 includes fore and aft body portions 130,132, and the fore portion is connected to the aft portion via anarticulation element 133. This element can be a hinge, pivot, orflexible body portion. The axis of articulation of the element can besubstantially perpendicular to a longitudinal axis of the platform, suchthat the axis of articulation is substantially horizontal. Articulationcan also be provided in a transverse direction (i.e., with an axis ofrotation about an axis substantially parallel to a longitudinal axis ofthe platform). The articulation element thus enables the fore portion toact as a “flipper” having selective (and controllable) contact with theterrain, so as to increase the stability of the vehicle when traversingrugged terrain or climbing or descending stairs.

[0072] Thus, the illustrated embodiment is an articulated, wheeledplatform, in which the articulation can be a substantially horizontalhinge forward of a fore/aft center of the platform. A total of eightwheels are arrayed substantially symmetrically about the plan-viewcenterline, and the centerline of articulation corresponds substantiallyto the second axle line, which is defined in this embodiment by theaxles coupled to wheel elements 114 and 112.

[0073] Moreover, in the embodiment depicted in FIGS. 1-7, wheels 112 and120 are rotatably coupled to the flipper, and the flipper can providesupport to the body (or other portion of the body) when traversingdifficult or steep terrain or stairs. Examples of the use of thearticulating body portions are shown in FIGS. 12B and 14-15C.Conventional angle control or motion control elements, such as electricmotors, can be provided to control the angle of the flipper portionrelative to the body as discussed in greater detail below.

[0074] In certain embodiments, the flipper is designed as to provide forincreased stability at various angles of deployment. In FIG.3, forexample, with the flipper 120 in a stowed position, the center ofgravity of the entire device preferably should be placed as close aspossible over the center of wheel element 124. Such a configurationminimizes the energy needed to propel the wheeled platform. Likewise,the flipper 120 should be weighted such that when the flipper isdeployed in a forward position, the center of gravity is movedsubstantially forward. This allows for greater stability over certainterrain, such as stairs and the like. In a preferred embodiment, thebatteries for the wheeled platform are arranged in the flipper 120 toallow for this movement of the center of gravity. One of skill in theart will recognize that the need to control the center of gravity may ormay not be necessary, depending on the size of the wheels and theexpected use of the platform

Increased Track of Intermediate Wheel Elements; Rocker

[0075] Also as most clearly shown in FIGS. 1A, 3, 5 and 7, in thisembodiment of the invention, at least one of the intermediate wheelelements on each side of the wheeled structure (whether there are one ormore intermediate wheels per side) are displaced outwardly from alongitudinal centerline of the body by an amount greater than that ofany end wheel element. In other words, in plan view, the centermostwheel or wheels elements have a wider “track” than the end wheelelements, and the port-side and starboard-side intermediate wheels, inplan view, are displaced outwardly from the body, relative to otherwheels in the respective first and second sets of wheel elements. Thisincreases the stability of the wheeled platform, while enabling theplatform to turn-in-place within a circle defined by the radii of theouter comers of the platform.

[0076] It will be noted that in the following detailed description andin the claims, the term “at least one intermediate wheel element” isused to denote one, two, three or more wheels per side (port andstarboard or left and right) that are longitudinally between “outer” or“comer” wheel elements. Similarly, the outboard or comer wheel elementscan number four or more. In an embodiment having four wheels, selectedwheel elements can be arbitrarily designated as intermediate wheelelements.

[0077] Also as most clearly depicted in FIGS. 1B and 1C, a selecteddegree of rocker is provided, such that the point of contact of at leastone intermediate wheel element on each side (in FIGS. 1A, 1B and 1C, thecenter wheel in each set of three wheels on the base portion of theplatform) can be lower than the respective point of contact of the endwheel elements. This reduces frictional losses when the platform istraversing smooth terrain and surfaces, and facilitates spinning orturning-in-place, thereby increasing agility of the platform.

Drive Elements

[0078] In a further aspect of the embodiment shown in FIGS. 1A, 1B and1C, drive elements are provided to drive the wheel elements and to drivethe flipper element. In one embodiment, an independent drive element isarranged to drive at least one respective wheel element, and controlelements are provided for controlling rotation of the respective wheelelements, to enable forward or reverse platform movement, turns orturns-in-place. Thus, a first set of wheel elements is coupled to a portside of the body, a second set of wheel elements is coupled to astarboard side of the body, and independent port-side and starboard-sidedrive elements are provided to enable forward and rearward movement,turns or turns-in-place. The wheel elements in selected sets (orsubsets) of wheel elements (e.g., left or right, port or starboard) canbe geared or otherwise mechanically coupled so that the wheels in awheel set turn in unison.

[0079] More particularly, as shown in FIGS. 1A, 1B, and 1C, drive module130 is coupled to the first set of wheels 102; drive module 131 iscoupled to the second set of wheels 104; and drive module 134 is coupledto the flipper portion, to raise and lower the flipper portion asrequired.

[0080] It will be understood that conventional power transmissionelements, such as shafts, couplings, gears, pulleys, belts, chains,clutches and the like, can be used as required in the illustratedembodiments, and the individual selection of particular drive elementsis within the ability of those skilled in the art.

[0081] It will also be recognized that there are various choices foractivating the propulsion and the articulation features of the disclosedplatforms. The illustrated platforms have three degrees of freedom,including port-side propulsion; starboard-side propulsion; andarticulation; and they are conveniently activated by using threeindependent motors. Moreover, in the illustrated embodiments (see, e.g.,FIG. 1A), one motor drives all port-side wheels through a reductiongearbox and a spur-gear train; a second motor drives all starboard-sidewheels through a second reduction gearbox and spur-gear train; and athird motor drives the articulation through a reduction gearbox and aworm-and-worm wheel train. In the wheeled-flipper embodiment, thearticulation axis is coincident with a wheel-and-spur gear axis (butthis is not necessary to practice the invention), so that the spur geartrain can bridge the articulation axis without any complication beyondan inconsequential interaction between actuation of the articulation andlimited rotation of the flipper-mounted wheels with respect to thebase-mounted wheels.

[0082] Finally, it will be recognized that numerous variations of thedisclosed structures and drive elements are possible, including, but notlimited to the use of three motors with different reduction andtransmission arrangements, such as jackshafts and universal jointsreplacing the spur gear trains of the illustrated embodiments; helicalgears instead of spur gears in the gear trains; or any combination orhybrid of the above. Also possible is the use of a motor, with orwithout reduction, for each wheel, as well as for the articulationaction; a single motor and two clutches, with or without reduction; ortwo motors and one clutch, with or without reduction.

“Tail” Embodiment

[0083] In another embodiment of the invention, depicted in FIGS. 8, 9,10, and 11, the wheeled platform 800 is equipped with an articulated“tail” element 802, pivotally coupled to a body portion 804, that can becontrolled to make selective contact with terrain. In a manner somewhatanalogous to the flipper portion of the embodiment shown in FIGS. 1-7,the tail element 802 can provide support to the body portion 804 whenthe platform 800 is traversing difficult or steep terrain or stairs.Thus, while in FIG. 8, the tail element is retracted, FIG. 9 depicts thetail element 802 in an extended position to make selective contact withterrain or surfaces. One of skill in the art will recognize that theembodiments comprising a flipper and embodiments comprising a tail arenot mutually exclusive.

[0084] Like the embodiment shown in FIGS. 1-7, platform 800 includesfirst and second sets (102, 104) of wheel elements that are rotatablyattached, respectively, to port and starboard sides of body portion 804,such that the corner wheel elements overlap the intermediate wheelelement in each set of wheel elements. In addition, the intermediatewheel element on each side is displaced outwardly from a centerline ofthe body portion 804. In this way, the intermediate wheel elements arewider apart than the comer wheel elements, and thus present a widertrack. This aspect is similar to that shown in plan view in FIG. 1A.

[0085] It will be understood that, among other things, fewer or morethan 6 wheels can be utilized, that the wheels may be spaced apart in anon-overlapping fashion, and that the wheels on each side may bedisposed all in a row, rather than offset (i.e., with the intermediatewheels wider apart than the corner wheels).

[0086] In the illustrated embodiment, the body portion 804 canaccommodate drive modules (which may include conventional batteries,electric motors, or the like) 806, 810 and transmission elements 812(which may include conventional gears, pulleys, belts, chains or thelike). The tail element 802 can be pivotally coupled to the body portion804 via a conventional articulation element 814, which can be aconventional pivot, hinge or the like. The angle and position of thetail element relative to the body portion 804 can be controlled by aconventional, dedicated motion control or drive element 807 (which canbe an electric motor or the like). Alternatively, the tail element canbe driven by a power take-off from a drive module 801 used to propel theplatform 800. Power is provided by battery 810.

[0087] Thus, the illustrated embodiment replaces the wheeled flipper ofFIGS. 1-7 with an articulated tail in the base's vertical fore-and-aftcenter plane. In the example shown, this configuration has six (6)wheels arrayed in a formation like that of the base of the first designconfiguration. The curved tail lying in the fore-and-aft vertical centerplane of the vehicle, and articulated about a laterally-disposedhorizontal axis that is typically at about or just aft the aft-most axleof the vehicle, is long enough to contact a step forward of the firstaxle of the vehicle, when the tail itself is articulated furthestforward with respect to the base. The articulated curved tail can beunder independent control, like the flipper of the first configuration.It may be used to contact the first step of a stairway and lift thefirst axle of the six-wheel three-axle base, off the ground or landing,and allowing it to attain the first step. Subsequently, the curvedarticulated tail may be swung all the way aft to contact the stairs aftthe vehicle, to enhance the vehicle's stability or orientation on thestairs. In a preferred embodiment, the tail 802 in its fully deployedaft position should remain at all times above the plane defined by thewheel elements to avoid interference with stairclimbing. While anarticulated tail in the described center plane may be a preferredembodiment, this embodiment of the invention can be configured with thearticulated tail in other planes or articulated about even skewed axes.

Non-Overlapping Wheels Embodiment

[0088] FIGS. 12A, 12B: In alternative embodiments of the invention,fore/aft wheel element overlap is not utilized, but instead, wheelelement diameter, wheel spacing, platform-to-wheel spatial displacement,and in one embodiment, flipper dimensions, are selected such that theplatform is sufficiently high to avoid contact with obstacles or terrainelements, such as stairs. In particular, the wheels in this embodimentare disposed sufficiently close together (but without overlap) such thatthe vehicle can transverse stairs, rocks, thresholds or other obstacles(in some instances, by employing a flipper element), while maintainingthe platform at a sufficient ground clearance to avoid ground/obstaclecontact.

[0089] Thus, for example, FIGS. 12A and 12B are schematic side views ofa wheeled platform 1200 in which the wheel elements are closely spaced,but without overlap. For purposes of simplicity, the present discussionand FIGS. 12A and 12B refer focus on one side (for example, the portside) 1201 of platform 1200. It will be understood, however, that thewheel elements and drive mechanisms depicted in FIGS. 12A and 12B can beduplicated, identically or non-identically, symmetrically orasymmetrically, on at least one other side (for example, the starboardside) of the wheeled platform 1200.

[0090] As shown in FIGS. 12A and 12B, wheeled platform 1200 includesbody or chassis portions 1202 and 1204 coupled together by at least onearticulation element 1206, which may be a conventional hinge, pivot, orflexible portion, having an axis of rotation substantially perpendicularto a longitudinal axis of the wheeled platform 1200. In the illustratedembodiment, wheels 1208, 1210, and 1212 are rotatably coupled to oneside 1201 (for example, the port side) of body portion 1204 byconventional elements (not shown), which may be like those discussedelsewhere in this document with respect to other embodiments of theinvention. In turn, wheels 1214, 1216, 1218 are rotatably coupled to oneside 1201 of body portion 1204.

[0091] In the example depicted, the axis of rotation of the articulationelement 1206 is substantially horizontal, so as to permit body portions1202, 1204 to move relative to one another in a substantially verticaldirection, thus increasing terrain compliance, as shown in FIG. 12B.This articulating ability of the wheeled platform 1200 may beadvantageously employed in ascending or descending pitches or stairs, asshown in FIG. 12B.

[0092] As in other embodiments discussed herein, motors or othermotion-control elements (not shown in FIGS. 12A and 12B) can be employedto control the angle of body portion 1204 relative to body portion 1202to facilitate ascending and descending, or reduce frictional losseswhile moving across relatively smooth surfaces.

[0093] The diameter of the wheel elements, wheel spacing,platform-to-wheel spatial displacement, and body portion dimensions canbe selected such that the platform is sufficiently high to avoid contactwith obstacles or terrain elements, such as stairs. In particular, thewheels in this embodiment are disposed sufficiently close together, andwheel diameter and platform-to-wheel displacement is selected such thatthe platform can transverse stairs or other obstacles, with the platformhaving sufficient ground clearance to avoid contact with the nose ofeach stair.

[0094] It will be understood that more than one articulation element canbe used, to further segment the body or chassis of the platform 1200,and that such articulation elements may have an axis of rotationsubstantially parallel to a longitudinal axis of the platform 1200. Inthis way, right/left or port/starboard articulation may be provided, inaddition to fore/aft articulation. In addition, more or fewer than 6wheels on each side may be utilized.

[0095] In this embodiment, the wheels on each side of the platform maybe disposed all in a row, rather than having the intermediate wheelsspaced wider apart (i.e., presenting a wider track) than the comerwheels. Alternatively, it may be useful to have at least oneintermediate wheel element on each side displaced outwardly, as in the“flipper” embodiment of FIGS. 1-7 and the “tail” embodiment of FIGS.8-11.

Patterned Wheel Elements

[0096] The use of one or more studded, scalloped or otherwise patternedwheel elements (or, in some cases, the tread portion of such wheelelements) at certain positions around the wheeled platform has beendemonstrated to be advantageous in certain applications. Examples ofsuch wheel elements are depicted in FIGS. 13A-13E. As shown therein,wheel elements 1300 that may be utilized in connection with theinvention may include a wheel portion 1302 having a hub 1304; and a tireportion 1306 having sidewalls 1308, 1310, and a tread portion 1312 thatcan be either smooth or patterned. This pattern, in turn, may bestudded, scalloped or other some similar pattern, whether regular orirregular, symmetrical or asymmetrical. One such pattern, shown in FIGS.13A-13E, consists of raised, spaced apart blocks 1314. The pattern shownin FIGS. 13A-13E has been demonstrated to be advantageous in platformsintended to travel frequently over bullnosed stairs, since the concavityof the scallop portion can effectively engage the rounded (bullnoses)leading edge of each stair-step, increasing traction and reducingslippage.

[0097] A particular practice of the invention utilizes scalloped wheelelements at the comers of the platform and smooth wheel elements for atleast one of intermediate wheel elements on each side. The use of smoothwheel elements at the intermediate or center positions on, for example,a 6-wheeled platform, facilitates spins and turn-in-place, whilemaintaining the terrain-handling advantages (e.g., stair-climbing)afforded by scalloped wheel elements at the 4 comers.

[0098] While the use of patterned wheel elements has been shown to beadvantageous in certain applications, it will be understood that theinvention can be practiced without the use of such wheel elements.Similarly, the invention can be practiced with different forms ofwheel/tire elements, and tires (as contrasted with wheel elements) canbe omitted.

Selection Criteria for Stair-Climbing

[0099] In the case of platforms useful in stair-climbing and descending,it has been found that the selection of wheel element diameter, axlecount and axle spacing can be made with recognition of the requirementsand vehicle dynamics of stair climbing and descending. FIGS. 14-15Cdepict various platform embodiment in accordance with the invention instair ascending/descending modes.

[0100] As depicted therein, in flipper embodiments, descents may beaccomplished with the platform arrayed flipper-first (“forward”), orflipper-last (“backward”). For forward descents, the flipper angle maybe controlled to prevent the platform from toppling off the landing atthe top of a flight of steps; or to smooth out the transition off thestairs onto the bottom landing, although neither operation is necessaryfor successful descents.

[0101] In typical operation on level, hilly or uneven ground, theplatform and its flipper can be operated as depicted in FIGS. 1B and14-15C, with the wheels of the flipper well clear of the ground. In apreferred embodiment, the center of gravity (CG) is well forward; andwith the forward CG, the platform at equilibrium on flat ground rests oroperates on the wheels of other axles.

[0102] The platform can address stairs in the same configuration, withthe flipper raised sufficiently for the wheels of the fore axle to climbover the first step. Once the first step is attained by the first axle,the articulated flipper can be lowered to horizontal, or slightly lower,with respect to the plane of the base, and the platform can proceed upthe stairs in this configuration, approximately as shown in FIGS.14-15C. A more active control of the flipper angle with respect to thebase can be useful for ascents of uneven steps, slippery stairs, or forsmoothness of operation, although such active control is not necessary.

CONCLUSION

[0103] The disclosed invention thus provides wheeled platforms ideallysuited to high-mobility, high-agility applications, including transport,robotic devices and the like, useful on rugged terrain, steep pitches,and stairs, whether indoors or outdoors. The structures disclosed arerobust, reliable, and conservative of battery or other energy sources,while providing enhanced abilities to traverse challenging terrain andascend or descend stairs and other obstacles. The disclosed platformscan be relatively compact, but scalable by selection of components andoverall dimensions to adapt to various expected (and unexpected) terrainrequirements.

[0104] It will be appreciated by those skilled in the art that thepresent invention may be practiced in connection with details thatdiffer from the specific examples of implementation set forth herein,and can be implemented in devices, systems and methods differing fromthose shown. Thus, the details set forth herein are provided by way ofillustration rather than limitation, and the invention is limited onlyby the scope of the appended claims.

We claim:
 1. A wheeled structure, comprising: a body having at leastfirst and second side portions, first and second sets of wheel elementsrotatably attached to the first and second side portions, respectively,wherein a portion of at least one wheel element on a first axis overlapsa portion of at least one other wheel element on a second axis in thesame set of wheel elements.
 2. The wheeled structure of claim 1 whereineach wheel element has a defined radius, and a portion of at least onewheel element in a set of wheel elements overlaps another wheel elementby a predetermined fraction of the radius of the other wheel element. 3.The wheeled structure of claim 1 wherein each set of wheel elements iscomprised of at least a first end wheel element, an intermediate wheelelement and a second end wheel element.
 4. The wheeled structure ofclaim 3 wherein each wheel element in a set of wheel elements has arespective transverse displacement from a longitudinal centerline of thebody, and the transverse displacement of the intermediate wheel elementis greater than that of the first end wheel element.
 5. The wheeledstructure of claim 4 wherein the transverse displacement of theintermediate wheel element is greater than that of the second end wheelelement.
 6. The wheeled structure of claim 3 wherein the intermediatewheel element in each set of wheel elements is always in contact withthe ground plane, and the first end wheel element and the second endwheel element are selectively in contact with the ground plane.
 7. Thewheeled structure of claim 1 further comprising an axle, rotatablycoupled to at least one wheel element, wherein the wheel element isrotatably coupled to the body at a greater transverse displacement froma longitudinal centerline of the body than at least one other wheelelement in the set of wheel elements.
 8. The wheeled structure of claim7 wherein each set of wheel elements is comprised of at least a firstend wheel element, an intermediate wheel element and a second end wheelelement, and wherein the intermediate wheel element is rotatably coupledto the body at a greater transverse displacement from a longitudinalcenterline of the body than at least one other wheel element in the setof wheel elements.
 9. The wheeled structure of claim 1 , wherein thebody comprises first and second body portions, the first body portionbeing connected to the second body portion via an articulation joint.10. The wheeled structure of claim 9 wherein the articulation joint is ahinge.
 11. The wheeled structure of claim 9 wherein the articulationjoint is a pivot.
 12. The wheeled structure of claim 9 wherein thearticulation joint is a flexible body portion.
 13. The wheeled structureof claim 9 wherein at least one wheel element from each set of wheelelements is rotatably coupled to each of the first and second bodyportions.
 14. The wheeled structure of claim 1 , wherein each set ofwheel elements is arrayed with a selected degree of rocker of the wheelelements coupled to the body, to enable the wheeled structure toturn-in-place.
 15. The wheeled structure of claim 1 , furthercomprising: an independent drive element arranged to drive at least onerespective wheel element; and control elements for controlling rotationof the respective wheel elements to enable longitudinal movement, turnsor turns-in-place.
 16. The wheeled structure of claim 1 , wherein atleast one wheel element is comprised of raised blocks spaced apartcircumferentially.
 17. The wheeled structure of claim 1 wherein at leastone wheel element is scalloped.
 18. The wheeled structure of claim 1wherein at least one wheel element is studded.
 19. The wheeled structureof claim 16 wherein the portion of at least one wheel element that iscapable of contact with the ground is substantially smooth.
 20. Thewheeled structure of claim 3 wherein at least a portion of theintermediate wheel element in each set of wheel elements issubstantially smooth, and at least the first and second end wheelelements in each set of wheel elements is comprised of raised blocksspaced apart circumferentially.
 21. A wheeled structure, comprising: abody having at least first and second side portions; first and secondsets of wheel elements rotatably attached to the first and second sideportions, respectively, wherein a portion of at least one wheel elementpartly overlaps a portion of at least one other wheel element in the setof wheel elements; and a flipper element pivotally coupled to a portionof the body, such that the flipper element can make selective contactwith a ground plane.
 22. The wheeled structure of claim 21 , furthercomprising at least one wheel element rotatably coupled to the flipperelement.
 23. The wheeled structure of claim 22 , further comprising amotion control element or controlling an angle of the flipper elementwith respect to the body.
 24. The wheeled structure of claim 23 whereineach wheel element has a defined radius, and a portion of at least onewheel element in a set of wheel elements overlaps another wheel elementin the set by a predetermined fraction of the radius of the other wheelelement.
 25. The wheeled structure of claim 24 wherein each set of wheelelements is comprised of at least a first end wheel element, anintermediate wheel element and a second end wheel element.
 26. Thewheeled structure of claim 21 further comprising an axle, rotatablycoupled to at least one wheel element in a set of wheel elements,wherein the wheel element is rotatably coupled to the body at a greatertransverse displacement from a longitudinal centerline of the body thanat least one other wheel element in the corresponding set of wheelelements.
 27. The wheeled structure of claim 26 wherein each set ofwheel elements is comprised of at least a first end wheel element, anintermediate wheel element and a second end wheel element, and whereinthe intermediate wheel element is rotatably coupled at a greatertransverse displacement from a longitudinal centerline of the body thanat least one other wheel element in the set of wheel elements.
 28. Thewheeled structure of claim 25 wherein the intermediate wheel element ineach set of wheel elements is always in contact with the ground plane,and the first end wheel element and the second end wheel element areselectively in contact with the ground plane.
 29. The wheeled structureof claim 21 further comprising an axle, rotatably coupled to at leastone wheel element in a set of wheel elements, wherein the wheel elementis rotatably coupled to the body at a greater transverse displacementfrom a longitudinal centerline of the body than at least one other wheelelement in the set of wheel elements.
 30. The wheeled structure of claim29 wherein each set of wheel elements is comprised of at least a firstend wheel element, an intermediate wheel element and a second end wheelelement, and wherein the intermediate wheel element is rotatably coupledat a greater transverse displacement from a longitudinal centerline ofthe body than at least one other wheel element in the set of wheelelements.
 31. The wheeled structure of claim 21 , wherein the bodycomprises first and second body portions, the first body portion beingconnected to the second body portion via an articulation joint.
 32. Thewheeled structure of claim 31 wherein the articulation joint is a hinge.33. The wheeled structure of claim 31 wherein the articulation joint isa pivot.
 34. The wheeled structure of claim 31 wherein the articulationjoint is a flexible body portion.
 35. The wheeled structure of claim 31wherein the first and second body portions each include at least onewheel of each set of wheel elements rotatably coupled to the respectivebody portion.
 36. The wheeled structure of claim 21 , wherein each setof wheel elements is arrayed with a selected degree of rocker of thewheel elements coupled to the body, to enable the wheeled structure toturn-in-place.
 37. The wheeled structure of claim 21 further comprising:an independent drive element arranged to drive at least one respectivewheel element; and control elements for controlling rotation of therespective wheel elements to enable longitudinal movement, turns orturns-in-place.
 38. The wheeled structure of claim 21 wherein at leastone wheel element is comprised of raised blocks spaced apartcircumferentially.
 39. The wheeled structure of claim 21 wherein atleast one wheel element is scalloped.
 40. The wheeled structure of claim21 wherein at least one wheel element is studded.
 41. The wheeledstructure of claim 21 wherein at least one wheel element issubstantially smooth.
 42. The wheeled structure of claim 25 wherein atleast the intermediate wheel element in each set of wheel elements issubstantially smooth, and at least the first and second end wheelelements in each set of wheel elements are comprised of raised blocksspaced apart circumferentially.
 43. The wheeled structure of claim 22 ,wherein the flipper element is pivotally coupled to the body to providesupport to the body when the wheeled structure traverses inclinedterrain.
 44. The wheeled structure of claim 22 , wherein the flipperelement is pivotally coupled to the body to provide support to the bodywhen the wheeled structure ascends stairs.
 45. The wheeled structure ofclaim 22 , wherein the flipper element is pivotally coupled to the bodyto provide support to the body when the wheeled structure descendsstairs.
 46. The wheeled structure of claim 22 wherein the wheel elementcoupled to the flipper element can make selective contact with a groundplane.
 47. A wheeled structure, comprising: a body, and a plurality ofwheel elements, each wheel element having a peripheral portion, thewheel elements being rotatably coupled to the body such that therespective peripheral portions of adjacent wheel elements overlap in anelevation view of the structure.
 48. The wheeled structure of claim 47 ,wherein the wheel elements are arrayed such that there is a selectedrocker of the wheel elements coupled to the body, to permit any ofenhanced turn-in-place or enhanced propulsion on level surfaces.
 49. Thewheeled structure of claim 48 wherein at least one wheel in a set ofwheels is coupled to the body with a transverse displacement from alongitudinal centerline of the body greater than that of other wheels inthe respective set of wheels.
 50. The wheeled structure of claim 49wherein the wheel coupled to the body with a greater transversedisplacement from a longitudinal centerline of the body is a centerwheel in the respective set of wheels.
 51. The wheeled structure ofclaim 47 further comprising: a first set of wheel elements coupled to aport side of the body, a second set of wheel elements coupled to astarboard side of the body, and independent port-side and starboard-sidedrive elements to permit forward and rearward movement, turns orturns-in-place.
 52. The wheeled structure of claim 51 , wherein theplurality of wheel elements includes, in plan view, port-side andstarboard-side center wheels, and the port-side and starboard-sidecenter wheels, in plan view, are displaced outwardly from the body,relative to other wheels in the respective first and second sets ofwheel elements.
 53. The wheeled structure of claim 52 , wherein at thewheel elements include any of studded or scalloped wheel elements. 54.The wheeled structure of claim 53 , wherein the body comprises first andsecond body portions coupled by an articulation element.
 55. The wheeledstructure of claim 47 , further comprising a flipper element coupled tothe body, for making selective contact with a ground plane.
 56. Thewheeled structure of claim 55 , further comprising at least one wheelelement, rotatably coupled to the flipper element, for making selectivecontact with the ground plane.
 57. The wheeled structure of claim 56 ,further comprising a motion control element for controlling movement ofthe flipper element in an angular direction with respect to the body.58. A wheeled structure comprising: front and back body portions coupledby an articulation element; a first set of wheel elements rotatablyattached to a first side of the wheeled structure, wherein a forwardwheel element in the first set of wheel elements is attached to thefront body portion, and a rear wheel element in the first set of wheelelements is attached to the back body portion; and a motion controlelement for controlling the relative position of each body portionaround the articulation element; wherein each wheel element has an axis,and the wheel element axes define a horizontal plane; and thearticulation element provides for pivoting movement between the frontand back body portions on an axis substantially parallel to thehorizontal plane of the body; and wherein the distance between one wheelelement on the front body portion and one wheel element on the back bodyportion is less than the radius of the smaller of the two wheelelements.
 59. The wheeled structure of claim 58 , further comprising asecond set of wheel elements rotatably attached to the right side of thewheeled structure, wherein a forward wheel element in the second set ofwheel elements is attached to the front body portion, and a rear wheelelement in the second set of wheel elements is attached to the back bodyportion;
 60. The wheeled structure of claim 59 wherein the articulationelement is a hinge.
 61. The wheeled structure of claim 59 wherein thearticulation element is a pivot.
 62. The wheeled structure of claim 59wherein the articulation element is a flexible body portion.
 63. Thewheeled structure of claim 59 , further comprising a flipper elementcoupled to the back body portion, for making selective contact with aground plane.
 64. The wheeled structure of claim 63 , further comprisingat least one wheel element, rotatably coupled to the flipper element,for making selective contact with the ground plane.
 65. The wheeledstructure of claim 64 , further comprising a motion control element forcontrolling movement of the flipper element in an angular direction withrespect to the body.
 66. The wheeled structure of claim 59 wherein eachwheel element in the set of wheel elements has a respective transversedisplacement from a longitudinal centerline of the body, and thetransverse displacement of the forward wheel element is smaller thanthat of another wheel element in the set of wheel elements.
 67. Thewheeled structure of claim 59 wherein the transverse displacement of therear wheel element is smaller than that of another wheel element in eachset of wheel elements.
 68. The wheeled structure of claim 59 wherein theintermediate wheel element in each set of wheel elements is always incontact with the ground plane, and the first end wheel element and thesecond end wheel element are selectively in contact with the groundplane.
 69. The wheeled structure of claim 59 further comprising an axle,rotatably coupled to at least one wheel element in the first set ofwheel elements, such that the wheel element is rotatably coupled to thebody at a greater transverse displacement from a longitudinal centerlineof the body than at least one other wheel element in the first set ofwheel elements.
 70. The wheeled structure of claim 59 wherein the firstset of wheel elements is further comprised of a center wheel elementset, and wherein at least one wheel in the center wheel element set isrotatably coupled to the body at a greater transverse displacement froma longitudinal centerline of the body than at least one other wheelelement in the first set of wheel elements.
 71. The wheeled structure ofclaim 59 , wherein the set of wheel elements is arrayed with a selecteddegree of rocker of the wheel elements coupled to the body to enable thewheeled structure to turn-in-place.
 72. The wheeled structure of claim59 , further comprising an independent drive element arranged to driveat least one wheel element, and a control element for controllingrotation of the wheel elements to enable longitudinal movement, turns orturns-in-place.
 73. The wheeled structure of claim 59 wherein the wheelelements in the set of wheel elements are geared so that the wheels in awheel set turn in unison.